Buying only the CD-Key, and some game suggestions.

[Tifone]

Nature gives you access to many supply-enhancing misc items under the Construction school. Nature mages themselves give a supply bonus in the province they are.
Also, Hinnom has very good PD (you can leave a province in your PD's relatively sure hands - also, remind that parking Hinnom's armies for long into a province is bad as commanders EAT your population there), and has very good units too - so you may feel comfortable in splitting your bigger armies into smaller armies to attack more territories a turn and reducing the need for high supplies. Also, their commanders can do as nice thugs, reducing your need for units.

I don't think there is a way to order just the CD-key, but I can bet Edi or llamabeast will be here soon to give you their greater knowledge and experience